I. Field of the Invention
The present invention relates to functional electrical stimulation (FES) of muscles to induce contraction thereof with electrical stimulus. More specifically, the present invention relates to electrically stimulating and exercising muscles to build muscle mass and, more particularly, isometric exercise of muscles associated with a limb which is adapted to rotate at a joint.
II. Background of the Invention
Much work has been done in the area of functional electrical stimulation of muscles. Most notably, substantial success has been achieved in the area of building muscle mass of nerve-disabled individuals such as paraplegics and/or quadriplegics by electrically stimulating the muscles sufficient to induce work-producing contraction of the muscles ("power contraction").
By way of example, U.S. Pat. No. 4,499,900, the disclosure of which is hereby incorporated herein by reference, discloses an exercise bicycle which utilizes functional electrical stimulation to induce sufficient contraction of lower trunk and leg muscles of a nerve-damaged individual such that the legs of that individual pedal an exercise bicycle thereby exercising otherwise atrophy-prone muscles. Because limbs are in motion, the exercise is referred to as isotonic.
Similar systems have been developed to provide isometric exercise of muscles, i.e., the associated limbs are not generally in motion. Characteristic of isometric exercise is that the limb is externally restrained from, or loaded against, rotation which would otherwise occur thus creating substantial torque at the joint about which the limb normally rotates. Prior art isometric exercise systems which utilized FES similarly restrained or loaded the involved limb. For example, U.S. Pat. Nos. 4,480,830 and 4,492,233, the disclosures of which are hereby incorporated herein by reference, disclose providing functional electrical stimulation to the muscles of a patient's leg to induce rotation of the lower leg at the knee joint. The ankle is restrained in one example so that the lower leg will not rotate. However, substantial torque may be created at the knee joint. To avoid overtorqueing the knee or damaging the limb of the lower leg and/or the knee joint, therefore, the level of electrical stimulation used for the isometric exercise must necessarily be limited. Consequently, loaded isometric exercise may impose limits on how much beneficial exercise can be obtained to build up muscle mass.
In systems of the prior art adapted to provide power contraction of human muscle, the electrical stimulus coupled to the muscle typically has characteristics which, if applied to an individual without severe nerve damage associated with the muscles to be stimulated, could cause excruciating pain. Thus, individuals who are either not nerve-damaged or have only partial (but relevant) nerve-damage may not be able to take full advantage of functional electrical stimulation without risking severe pain. Thus, use of prior art "power contracting" type of systems have generally been limited to paraplegics and/or quadriplegics. However, many individuals, not just those suffering from severe nerve damage, could benefit from electrically-induced power contraction exercise therapy.